V. G. Zhukov

Organization of metabolic pathways and molecular-genetic mechanisms of xenobiotic degradation in microorganisms: A review

Contemporary data on the mechanism of biodegradation of aromatic hydrocarbons and biodegradation genes (genomic organization and pathways of evolution) in diverse groups of microorganisms have been reviewed. Studies of this problem are topical, in view of the need in identification and construction of new strains degrading xenobiotics, particularly those halogenated. For this reason, emphasis is placed on specific features of explored metabolic pathways that can be used for constructing new enzymatic systems not present in nature. Sections on the mechanisms of genomic rearrangements involving biodegradation determinants are presented from the same standpoint. Part of the review is devoted to analyzing methods used for studying the population dynamics of bacterial communities involved in xenobiotic degradation in natural biotopes or industrial waste disposal plants. Particular attention is given to methods of gene systematics.

Application of molecular systematics to study of bacterial cultures consuming volatile organic compounds

A range of species of four mixed bacterial cultures was studied by molecular systematics methods with the use of 16S rRNA genes. The cultures had been developed for application in minireactors, to degrade volatile organic compounds (VOCs): ethyl benzene, m-xylene, styrene, and o-xylene. A sample of 30 plasmid rDNA clones was obtained for each of the mixed cultures. The clones were analyzed by RFLP according to two restriction sites. Major variants of the 16S-rDNA sequences, corresponding to the most abundant species, were determined for each association. Sequencing of four clones of predominant 16S-rDNAs showed that the culture consuming ethyl benzene was dominated by Pseudomonas fluorescens; o-xylene, by Achromobacter xylosoxydans; styrene, by Pseudomonas veronii; and m-xylene, by Delftia acidovorans. Minor components of all four cultures were generally similar. They included species of the genera Sphingobacter, Rhizobium, Mesorhizobium, Pedobacter, and Paenibacillus. Sampling sequencing of genes for 16S rRNA cloned from total genomic DNA allowed quantitative determination of the composition of actual bacterial associations consuming VOCs in minireactors.

Odor Removal in Industrial Facilities

Air pollution, once the concern of only large urban settlements, is rapidly spreading worldwide and becoming one of the major challenges of modern civilization. Greenhouse gases, harmful and hazardous inorganic and volatile organic compounds (VOCs), nauseous odors – these are just some of the problems to be solved to ensure a healthy and comfortable environment for future generations. The principal sources of modern air pollution are vehicles, industrial sites, and municipal facilities dealing with water treatment, collection and disposal of waste, etc. (Table 14.1). There are several approaches to the problem. The preferred solution is, of course, the development of new “green” technologies that impose less burden on the environment, and the use of new, cleaner energy sources, including nonconventional ones. Nevertheless, efficient abatement technologies, i.e., endof-pipe solutions, will in the near future remain an essential tool for reducing air pollution. Whatever future advances wemake in industrial production, one element of moderncivilizationwill continue toaggravateairpollution.Mankindgenerates more andmore waste, and its collection, disposal and recycling is a substantial factor in the sustainable development of our economies. All these activities generate various odors and smells that are detrimental to the environment and quality of life. These problemswill persist indefinitely, and the only foreseeable remedy is the development of efficient and economical ways to treat these sources of air pollution. Biological methods of air purification are indispensable when large and diluted volumes of VOCs and|or odor-laden air are to be treated (Cox and Deshusses 1998; Devinny et al. 1999; Cox and Deshusses 2000; Shareefdeen et al. 2003). Their main advantages over traditional methods (incineration, activated carbon adsorption, etc.) are well known and mainly reside in low operational costs. Moreover, they do not generate secondary waste streams and|or pollutants, and are readily accepted by regulating authorities and the general public. Biofiltration has been successfully used to neutralize odors of different origin (agricultural, municipal, industrial) containing sulfur and nitrogen compounds, and to remove an impressive number of various volatile

Metabolic pathways responsible for consumption of aromatic hydrocarbons by microbial associations: Molecular-genetic characterization

Genes for catechol 1,2- and 2,3-dioxygenases were cloned. These enzymes hold important positions in the ortho and meta pathways of the metabolism of aromatic carbons by microbial associations that consume the following volatile organic compounds in pilot minireactors: toluene, styrene, ethyl benzene, o-xylene, m-xylene, and naphthalene. Genes of both pathways were found in an association consuming m-xylene; only genes of the ortho pathway were found in associations consuming o-xylene, styrene, and ethyl benzene, and only genes of the meta pathway were found in associations consuming naphthalene and toluene. Genes of the ortho pathway (C12O) cloned from associations consuming o-xylene and ethyl benzene were similar to corresponding genes located on the pND6 plasmid of Pseudomonas putida. Genes of the ortho pathway from associations consuming o-xylene and m-xylene were similar to chromosomal genes of P. putida. Genes of the meta pathway (C23O) from associations consuming toluene and naphthalene were similar to corresponding genes formerly found in plasmids pWWO and pTOL.

Elimination of volatile compounds of leaf tobacco from air emissions using biofiltration

The composition of the volatile organic compounds (VOCs) of various leaf tobacco brands and their blends has been studied. The differences in the content of nicotine, solanone, tetramethyl hexadecenol, megastigmatrienones, and other compounds, determining the specific tobacco smell, have been revealed. A microbial consortium, which is able to deodorize simulated tobacco emissions and decompose nicotine, has been formed by long-term adaptation to the VOCs of tobacco leaves in a laboratory reactor, functioning as a trickle-bed biofilter. Such a biofilter eliminates 90% of the basic toxic compound (nicotine) and odor-active compounds; the filtration efficiency does not change for tobacco brands with different VOC concentrations or in the presence of foreign substances. The main strains, isolated from the formed consortium and participating in the nicotine decomposition process, belong to the genera Pseudomonas, Bacillus, and Rhodococcus. An examination of the biofilter trickling fluid has shown full decomposition of nicotine and odor-active VOCs. The compounds, revealed in the trickling fluid, did not have any odor and were nontoxic. The obtained results make it possible to conduct scaling of the biofiltration process to eliminate odor from air emissions in the tobacco industry.